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Calcium intake in Western countries
International 0 1992
Journal of Cardiology,
227
34 (1992) 227-228
Elsevier Science Publishers B.V. All rights reserved 0167-5273/92/$05.00
CARD10 01395
Letter to the Editor
Calcium intake in Western countries 25 September
1991
Sir, May I make some comments on the paper of S. Seely in your November 1991 issue? (Int J Cardiol 1991;33:191-1981. One of the subjects of the paper is the action of phytic acid on dietary calcium. This may not have been correctly interpreted in the past. The calcium in food need not always be in a form to react readily with phytic acid, whereas that in saliva might be. Thus, it is possible that phytic acid is targeted on the saliva and other digestive fluids of animals, rather than the food. The quantity of calcium lost in this manner is very difficult to estimate. Phytic acid is destroyed by the leavening of bread, and wholemeal flour contains more of it than white flour. Also, mastication is only a superficial mixing process, more so in quick eaters than in slow eaters. There must be considerable individual differences in the proportion of dietary calcium lost through the action of phytic acid. Apart from the action of phytic acid, the calcium content of digestive fluids is unlikely to be completely reabsorbed from the intestines. A rough estimate of the loss can be made by assuming that, while the calcium content of the various digestive fluids is different, when they are all mixed in the small intestines, their calcium concentration is the same as that of the plasma, disregarding the non-diffusible (protein bound) calcium content of the latter. The daily production of digestive fluids consists of 1.5 litres of saliva, 3 litres of gastric juice and 2 litres of pancreatic fluid, making a total of 6.5 litres. At 55 mg/litre their total calcium content is about 360 mg. If, as a guess, it is assumed that 60 mg of this is lost through the action of food acids, and 20% of the remaining 300 mg is lost on reabsorption from the intestines, a total loss of 120 mg/day arises on this account. If this is added to the daily calcium requirements of young adults estimated by Seely at 250 mg, the total is 370 mg, corresponding to a daily dietary requirement of about 500 mg. This is not very far from the 525 mg recommended by the
COMA report (Lancet Noticeboard, July 13, 1991, p. 111). I do agree with Seely that individuals who consume more than a pint of milk daily (or its equivalent in dairy products), can have a calcium intake of about 1000 mg, and calcium supplements taken by some individuals can add another 1000 mg to that. Calcium intake in advanced countries does tend to be excessive, even if Seely made the excess somewhat bigger than it really is by not taking all losses into account. latest
Univ. of Manchester Dept. of Chemistry Manchester, U.K.
Gerald A. Silverstone
Reply : Sir, Dr. Silverstone’s letter puts forward the interesting suggestion that phytic acid, produced by several cereals and other plants as a secondary metabolite, may be targeted not so much on the content of calcium in foods, but on that of the saliva and other digestive fluids. Presumably, the calcium in foods is contained mainly in the form of salts, that in the saliva in form of ions, even if in a buffered, neutral solution. The suggestion that this may more readily react with phytic acid than calcium salts seems reasonable and should be investigated. If the suggestion is correct, phytic acid would be a more potent calcium antagonist than previously thought. When writing my paper on above subject, I, like everybody else, was of the opinion that phytic acid reacted with calcium in food. If so, it would not directly affect the daily requirements of the body for calcium. Presumably the term “dietary calcium intake” means calcium in an absorbable form. Indigestible compounds, like calcium carbonate or oxalate, can be taken as non-foods. If, on the other hand, phytic acid interferes with digestive fluids, it causes a loss of calcium which must be replaced.
Journal of Cardiology,
227
34 (1992) 227-228
Elsevier Science Publishers B.V. All rights reserved 0167-5273/92/$05.00
CARD10 01395
Letter to the Editor
Calcium intake in Western countries 25 September
1991
Sir, May I make some comments on the paper of S. Seely in your November 1991 issue? (Int J Cardiol 1991;33:191-1981. One of the subjects of the paper is the action of phytic acid on dietary calcium. This may not have been correctly interpreted in the past. The calcium in food need not always be in a form to react readily with phytic acid, whereas that in saliva might be. Thus, it is possible that phytic acid is targeted on the saliva and other digestive fluids of animals, rather than the food. The quantity of calcium lost in this manner is very difficult to estimate. Phytic acid is destroyed by the leavening of bread, and wholemeal flour contains more of it than white flour. Also, mastication is only a superficial mixing process, more so in quick eaters than in slow eaters. There must be considerable individual differences in the proportion of dietary calcium lost through the action of phytic acid. Apart from the action of phytic acid, the calcium content of digestive fluids is unlikely to be completely reabsorbed from the intestines. A rough estimate of the loss can be made by assuming that, while the calcium content of the various digestive fluids is different, when they are all mixed in the small intestines, their calcium concentration is the same as that of the plasma, disregarding the non-diffusible (protein bound) calcium content of the latter. The daily production of digestive fluids consists of 1.5 litres of saliva, 3 litres of gastric juice and 2 litres of pancreatic fluid, making a total of 6.5 litres. At 55 mg/litre their total calcium content is about 360 mg. If, as a guess, it is assumed that 60 mg of this is lost through the action of food acids, and 20% of the remaining 300 mg is lost on reabsorption from the intestines, a total loss of 120 mg/day arises on this account. If this is added to the daily calcium requirements of young adults estimated by Seely at 250 mg, the total is 370 mg, corresponding to a daily dietary requirement of about 500 mg. This is not very far from the 525 mg recommended by the
COMA report (Lancet Noticeboard, July 13, 1991, p. 111). I do agree with Seely that individuals who consume more than a pint of milk daily (or its equivalent in dairy products), can have a calcium intake of about 1000 mg, and calcium supplements taken by some individuals can add another 1000 mg to that. Calcium intake in advanced countries does tend to be excessive, even if Seely made the excess somewhat bigger than it really is by not taking all losses into account. latest
Univ. of Manchester Dept. of Chemistry Manchester, U.K.
Gerald A. Silverstone
Reply : Sir, Dr. Silverstone’s letter puts forward the interesting suggestion that phytic acid, produced by several cereals and other plants as a secondary metabolite, may be targeted not so much on the content of calcium in foods, but on that of the saliva and other digestive fluids. Presumably, the calcium in foods is contained mainly in the form of salts, that in the saliva in form of ions, even if in a buffered, neutral solution. The suggestion that this may more readily react with phytic acid than calcium salts seems reasonable and should be investigated. If the suggestion is correct, phytic acid would be a more potent calcium antagonist than previously thought. When writing my paper on above subject, I, like everybody else, was of the opinion that phytic acid reacted with calcium in food. If so, it would not directly affect the daily requirements of the body for calcium. Presumably the term “dietary calcium intake” means calcium in an absorbable form. Indigestible compounds, like calcium carbonate or oxalate, can be taken as non-foods. If, on the other hand, phytic acid interferes with digestive fluids, it causes a loss of calcium which must be replaced.